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 Post subject: coolant temp sensor - no readings... pretty odd
PostPosted: Thu Apr 10, 2008 5:00 pm 
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Joined: Sat Oct 13, 2001 4:53 pm
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Location: Erlangen <=> Coburg
Hey guys, i have a pretty odd problem with my coolant temp sensor.
Last year, right before i put the convertible into storrage for winter, the temp gauge stopped working (needle way below 100F), the fans came on all the time and as i smell unburned fuel, i guess the car went into dummy/safe mode. I cleaned the pcm terminals, sensor connector etc, and it worked again.
Well, till yesterday.

I used a circuit indicator to check the wiring from the PCM terminal to the sensor connector, both wires are fine.
I measured the resistance on the sensor directly on the PCM connector, the values make sense and it seems like it's working.
I replaced the sensor with a resistor to simulate 200F, when i now turn the key to position one the temp gauges starts climbing to around 150 and then suddenly falls again below 100F like theres no resistor.
It doesn't do that without the resistor and simply stays below 100F.
With the resistor in place it also turns the fans on to cool the car down as if it was hot after running.

Nevertheless, the fans come on all the time with the resistor in place when i start it, even if i "simulate" a lower temperature and the gauge still doesn't work - so i guess it somehow doesn't get any readings.

-ANY- ideas what i could do next or what the problem could be?
(Except setting the car on fire, what i really like to do right now.)
Thanks a lot.

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 Post subject: Re: coolant temp sensor - no readings... pretty odd
PostPosted: Thu Apr 10, 2008 7:11 pm 
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Location: Mehlingen,Rhineland Pfalz, Deutschland
Chris
Sorry you got me stumped, with out a tech manual and some trouble shooting.

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 Post subject: Re: coolant temp sensor - no readings... pretty odd
PostPosted: Sat Apr 12, 2008 1:51 pm 
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Joined: Sat Oct 13, 2001 4:53 pm
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Location: Erlangen <=> Coburg
Nevertheless thanks for the reply ;)

Well, i now replaced both wires running from the PCM connector to the sensor, no change, the SES light comes on right when you turn the key to the first position, even if i disconnect the battery for a long time (which should erase the errors, right?).
And the sensor resistance definitely changes with temperature, that thing works. I have two other GM ECT sensors in my garage,
i'm going to replace it just to rule it out, but...well.

Anybody near Nürnberg or Bamberg with a code scanner?

As i still have to drive my car a bit, how harmfull is the dummy mode for the engine? I can smell that it runs quite rich, which can't be good for the oiling, but otherwise...?

If i have to replace the PCM (just in theory) does it have to be flashed for my car (immobilizer etc etc?) or will any 1998 to 2002 3.8 A4 PCM work right away like plug&play?

Thanks...

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2001 Pontiac Firebird Convertible 3.8l V6 - daily cruiser
1994 Pontiac Firebird 3.4l V6 - new engine one the way
1990 Chevy Beretta GTZ, back on the road in the year 2057


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